1. Field of the Invention
The present invention is related to a process for preparing aliphatic or cycloaliphatic epoxy resins.
2. Description of Background and Related Art
Epoxidation of aliphatic and cycloaliphatic alcohols is an area of long standing interest, for example as described in EP 0 121 260. Disclosed in EP 0 121 260 are examples of phase transfer catalyzed epoxidation of aliphatic diols using quaternary ammonium halide catalysts with epichlorohydrin, including cyclohexanedimethanol (isomers unspecified).
Chemistry and processes for the manufacture of aliphatic and cycloaliphatic epoxy resins via epoxidation of aliphatic and cycloaliphatic hydroxyl containing materials using an epihalohydrin is difficult, if not impossible, to drive to full conversion and produces significant quantities of partially epoxidized products, such as, for example, monoglycidyl ether (MGE) (as much as 2-20 weight percent (wt %) of the epoxy resin composition), as well as oligomeric co-products (as much as 25-40 wt % of the epoxy resin composition). While various methods, such as, for example, distillation, are operable for removal of unconverted aliphatic and cycloaliphatic hydroxyl containing reactant, MGE, diglycidyl ether (DGE) product, and the like, no satisfactory solution exists for dealing with partially epoxidized products such as MGE, once removed.
Another complication is that while the recovered unconverted aliphatic and cycloaliphatic hydroxyl containing reactant may be reused as reactant in a new epoxidation, most methods used for recovery will only provide aliphatic and cycloaliphatic hydroxyl containing reactant containing a contaminating amount of MGE. Likewise, most methods used for removal and recovery of MGE will only produce a product containing both MGE and DGE.
The best solution to date has been use of the aliphatic and cycloaliphatic epoxy resins as reactive diluents for epoxy resins where the unreacted aliphatic and cycloaliphatic hydroxyl containing material, MGE, the desired DGE and the oligomeric co-products are simply carried into the total diluent and epoxy resin composition. Problems with this approach include (1) reduction of mechanical properties induced by any unreacted aliphatic and cycloaliphatic hydroxyl containing material or even leaching of said material from a thermoset product, (2) reduction of reactivity with curing agents and chain termination caused by monofunctionality of the MGE resulting in reduction of mechanical properties, and (3) higher than desirable viscosities induced by the presence of the oligomeric co-products and reduced reactivity with curing agents.
Thus, it would be highly desirable to be able to fractionate an aliphatic or cycloaliphatic epoxy resin to specifically provide DGE for use as a low viscosity and highly reactive epoxy resin diluent or reactant for epoxy resin advancement while simultaneously providing a viable end use for any MGE plus unreacted aliphatic and cycloaliphatic hydroxyl containing material, MGE, and MGE plus DGE fractions that result. It should be noted that the aforementioned discussion centers upon epoxidation processes where the aliphatic and cycloaliphatic hydroxyl containing material is a diol, however, the term “aliphatic and cycloaliphatic hydroxyl containing material” is intended to include higher functional materials such as triols.
WO/2009/142901, incorporated herein by reference, describes an epoxy resin composition prepared from a mixture of cis-, trans-1,3- and 1,4-cyclohexanedimethanols using a wide variety of epoxidation processes. Additionally demonstrated in the examples of WO/2009/142901 is the preparation of various distilled grades of the MGE and DGE of cis-, trans-1,3- and 1,4-cyclohexanedimethanols, including high purity (>99 wt %) DGE.
Typically, in preparing the high purity DGE product by the process of WO2009/142901, a residual amount of unreacted aliphatic or cycloaliphatic diol, MGE, DGE, and oligomeric products are formed during the reaction process disclosed in WO2009/142901. Thus, distillation methods are typically employed after the epoxidation process of WO2009/142901 in order to remove the unwanted unreacted aliphatic or cycloaliphatic diol, MGE, and any other higher boiling oligomeric materials from the desired the DGE product. The resulting high purity DGE can then be used in the aforementioned advancement chemistry or as a reactive epoxy resin diluent.
After the desired high purity DGE product is substantially removed using a distillation column as taught in the WO2009/142901 process, an undesired co-product produced from the distillation process usually includes (1) an unreacted aliphatic or cycloaliphatic diol stream containing minor amounts of MGE, (2) a MGE stream, and (3) a MGE and DGE stream. Generally, in order for a process for preparing purified DGE to be industrially practical and commercially viable, something useful must be done with the unwanted co-products such as the co-produced unwanted MGE containing fractions from the distillation process in order to recover the value from such co-products.
Extensive research is ongoing to develop can coating resins based on high purity DGE of cycloaliphatic hydroxyl containing materials such as UNOXOL™ Diol. [UNOXOL™ cyclic dialcohol is a registered trademark of Union Carbide Corporation.] The scale-up of the epoxidation of UNOXOL™ Diol normally yields significant quantities of the MGE and MGE/DGE fractions from the distillation operation to recover high purity DGE. It would be desirable to find a process for handling the resultant MGE and MGE/DGE fractions from distillation without detrimentally impacting the epoxidation reaction process to produce high purity DGE for the can coating applications.
Heretofore, a process for the specific recycle of the MGE containing fractions obtained, for example, from the distillation of an aliphatic or cycloaliphatic epoxy resin into an epoxidation to recover useful products from said MGE containing fractions has not been done before in an epoxidation process for aliphatic and cycloaliphatic hydroxyl containing materials.
It is therefore desired to provide a process for recovering the MGE containing fractions from the fractionation of an aliphatic or cycloaliphatic epoxy resin and recycling the MGE containing fractions into an epoxidation reaction process for converting the MGE into useful materials such as DGE or polyfunctional aliphatic or cycloaliphatic epoxy resin.